The subject invention is directed toward the art of pipes and tubular conduits and, more particularly, to a method of forming a chamfered end on a pipe.
The invention is especially suited for forming a chamfered spigot end on large diameter spiral wound plastic pipe and will be described with reference thereto; however, as will become apparent, the invention is capable of broader application and could be used on many types of pipe and for forming either bell or spigot ends.
In U.S. Pat. No. 3,926,223, there is illustrated a pipe construction which is particularly suited for forming large diameter pipe suitable for use as water or sewage pipe. The construction consists of a multiplicity of helical turns of an extruded thermoplastic synthetic resin strip having a cross-section with a hollow, generally rectangular form. The strip is extruded and coiled in a helical path. Adjacent turns of the helix are butt-welded to produce a continuous spiral wound pipe structure. The resulting pipe structure effectively constitutes a pair of radially spaced inner and outer side walls joined by a radially extending helical intermediate wall which forms a continuous helical chamber extending the length of the pipe. The method and apparatus used in constructing the pipe is more particularly shown and described in U.S. Pat. Nos. 3,917,500 and 4,033,808.
In the U.S. and most western countries the accepted method of connecting large diameter sewer and water pipe is through the use of rubber gasketed, bell and spigot pipe end construction. In order to produce a tapered or chamfered spigot end on the pipe, it has been the practice to simply machine a chamfer on the spigot end thereby exposing the helical inner wall. The exposed inner wall and the exposed portion of the helical chamber were then filled with a rigid, two part acrylic system.
The prior method produces an acceptable chamfered spigot end but it is both time consuming and expensive. In addition, the rigid acrylic filler reduces the flexibility of the pipe ends and makes them susceptible to breakage during handling and installation. As can be seen from the foregoing, a need exists for a more satisfactory method of forming and sealing the ends on spiral wound pipe.